1. All mineral substances in their fixed, that is, in their crystaline form, are angular with flat sides and straight edges. This is not only a general rule and an approximate statement, but exactly accurate and universal; for in the few instances of crystals occurring with convex or curvilinear faces, such as the diamond, it is known that their primary forms have plane or flat faces and a parallel cleavage—making the rule good against accidental influences and superficial appearances.
Here then we have a mode of configuration appropriate to and distinctive of one whole kingdom of nature.
2. In vegetables we have a different figure and characteristic conformation. Their trunks, stems, roots and branches are nearly cylindrical, and uniformly so, in all individuals clearly and completely within the class.
Soon as we enter the precincts of life curvature of lines and convexity of surface begin to mark the higher styles of existence, the law being that nothing which lives and grows by the reception and assimilation of food is angular, rectilinear or included within plane surfaces. Inert bodies take straight, but life assumes curve lines.
3. In animal forms the curve or life line is present of necessity, but it undergoes such modification and departure from that which marks vegetable existence as our law demands. We no longer have almost cylindrical simplicity of shape as the sign of character and kind, but, retaining curvity, which is common to vitality of all modes, we find the cylinder shaped or tapered toward the conical, with continually increasing approach to a higher style of configuration as we ascend toward a higher character of function.
In the human body all that belongs to the whole inferior creation is represented and reproduced, for man is logically a microcosm, and in his body we find the various orders of natural beings marked by their appropriate modes of construction and configuration—from a hair to a heart, the multifarious parts bring with them the forms native to their respective varieties of being.
The bones have in them the material of the mineral kingdom, and they have conformity of figure. In the short, square bones of the wrist, in the teeth, and several other instances, the flatness, straightness and angularity proper to crystalized matter, marks its presence as an element of the structure.
The correspondence of the vascular system with the forms proper to vegetation, is most striking. A good drawing of the blood vessels is a complete picture of a tree. Now, animals and vegetables differ widely in their manner of taking in food, but they are alike in the method and end of the distribution of the nutritious fluids, and between them the resemblance of form obtains only in this, as our law requires. There is nothing in trees, shrubs or grasses, that has any outline likeness to the esophagus, stomach or intestinal tube; nothing in them has any resemblance of office, and nothing, therefore, is formed upon their pattern. The roots of trees, which are the avenues of their principal aliment, are merely absorbing and circulating instruments—a sort of counterpart branches in function—and they have, therefore, what scientific people call the arborescent arrangement wherever they find it.
If it is answered here that a hydraulic necessity determines the general form of circulating vessels, and that certain immediate mechanical advantages belong to the cylindrical over the square or polygonal shape of tube, our point is not affected. We are showing, now, that the expected conformity never fails. It is essential to our position that mechanical requirements shall not over-rule the general law. The instance given is in accordance, and a presumption rises that even mechanical conformation itself is covered and accommodated by the great principle which we are illustrating. It is enough for us, however, that no facts contradict, though it be doubted whether all the instances cited afford us the expected support.
But, leaving the functions and organs, which belong to all living and growing beings in common, and entering the province of animal life and animal law proper, we everywhere observe a significant departure from the angular and cylindrical forms of the mineral and vegetable kingdoms, and an approach, in proportion to the rank and value of the organ and its use, toward an ideal or model, which is neither conical nor heart-shaped, exactly, but such a modification of them as carries the standard figure farthest from that uniformity of curve which marks a globe, from the parallelism of fibre which belongs to the cylinder, and from the flatness of base and sharpness of apex which bound the cone.